The reference manual says "Refer to the device data sheet for filter characteristics.", but the device data sheet does not have the word "passive" anywhere.
I've seen a similar question asked about the KL25 but the "correct answer" for that thread simply says "This filter is not the traditional filter. It is not high frequencty filter nor band filter. It can looks like a pulse counter. It will delete small width pulse. So it looks like a filter."
I'm really hoping for more information here, preferably with actual numbers!